The invention relates to filter bodies for entrapping solic particulates and larger contaminants present in fluids and, in particular, to filters of new configurations and methods for forming such filters from thin porous walled, honeycomb structures.
The removal of solid particulates from fluids, gases or liquids, in which the particulates are mixed or suspended is typically accomplished by means of filters made from solid materials which are formed into articles or masses having a plurality of pores of small cross-sectional size extending therethrough, which may be interconnected, such that the solid materials are both permeable to the fluids which flow through the article or mass and capable of restraining some or all or substantially all of the particulates mixed in the fluid from passing through the article or mass, as desired. Such pores constitute what is termed "open porosity" or "accessible porosity". Particulates are collected on the inlet surface(s) and/or within the pores of the material. The minimum cross-sectional size of some or all of the pores can be larger than the size of some or all of the particulates to be removed from the fluid, but only to the extent that significant or desired amounts of sufficiently large particulates become trapped on or within the filters during the transit of contaminated fluid. As the mass of collected particulates increases, the flow rate of the fluid through the filter generally decreases to an undesirable level. The filter is then either discarded as a disposable, replaceable element or regenerated by removing the collected particulates. Desirable features of the filter include compact structure, mechanical integrity, durability, inertness or non-deleterious reaction with the fluid and/or particulate material.
For some time solid particulate filter bodies have been formed from honeycomb structures. Ser. No. 165,646, filed July 3, 1980 and assigned to the assignee hereof, and U.S. Pat. Nos. 4,276,071, both incorporated by reference herein, describe essentially unidirectional flow solid particulate filters formed from honeycomb structures each having a matrix of thin, porous, intersecting walls defining a pair of open, end faces on opposing outer surfaces of the structure and a multiplicity of cells extending longitudinally through the structure in a substantially mutually parallel fashion between the end faces. At each end face where the open transverse areas of the cells would normally be exposed, the ends of alternate cells are closed in a checkered or checkerboard pattern. The pattern of alternate closed cell ends is reversed at either end face so that each cell of the structure is closed at only one end face and shares thin walls in common with adjoining cells which are closed only at the opposing end face of the structure. A contaminated fluid introduced under pressure to an "inlet" end face of the filter body passes into those cells open at the inlet end face ("inlet" cells). Because the inlet cells are closed at the opposing "outlet" end face of the structure, the contaminated fluid is forced to pass across the narrow dimension of the thin, porous walls into the adjoining "outlet" cells (which are all closed at the inlet end face and open at the outlet end face of the structure) and through the outlet cells to and through the outlet end face of the filter. The solid particulate matter in the fluid, or that portion which is sufficiently large, is eposited on the thin wall surfaces defining the interior of the inlet cells or is trapped in the pores forming the interconnected open porosity of the thin walls. All of the contaminated fluid passing through the structure is filtered and all of the interconnected, thin walls of the structure, each of which is shared in common between an adjoining inlet and outlet cell, are utilized in filtering.
Various methods and/or apparatus have been devised to close the ends of selected cells at each open end face of a honeycomb structure by plugging and, in some cases, by covering cell ends. The application Ser. No. 165,646 describes plugging selected cell ends at each end face of a honeycomb structure using an air actuated cement charging gun, the nozzle of which must be aligned with each cell end to be closed. Other methods and apparatus are described and claimed in the following pending application Ser. Nos. 283,732, 283,733 283,734 and 283,735 filed July 15, 1981, and 295,610 and 295,611, both filed Aug. 24, 1981, all assigned to the assignee hereof and incorporated by reference herein. In application Ser. No. 295,611, all cell ends at an end face of the honeycomb structure were temporarily plugged and plugs in selected cells were moved through or removed from the structure by apparatus aligned with the selected cell ends. In application Ser. No. 283,732, a solid covering was applied to the open end face of a honeycomb structure and openings made through the covering by a tool aligned with selected cell ends sensed beneath the covering. Application Ser. No. 283,733 describes plugging honeycomb structures to form solid particulate filter bodies using a mask comprising a solid covering having a plurality of openings extending through it each of which has to be formed or aligned opposite a cell end selected to be plugged. Plugging material was passed through the mask openings and into the selected cell ends completing their closure. Application Ser. No. 295,610 describes two improved mask embodiments in which protrusions or plugs forming a portion of the mask had to be aligned with and inserted into selected cell ends. Application Ser. No. 283,734 describes flexible and elastic masks having openings extending therethrough and protrusions extending therefrom, the latter being inserted into and temporarily sealing cell ends not to be plugged and serving to align the mask openings with other cell ends selected for plugging.
One problem associated with each of these inventions is that like the air gun method of the application Ser. No. 165,646, each requires that a tool be aligned with or, in the case of a mask, openings formed or aligned opposite and/or, in certain cases, protrusions aligned with and inserted into the ends of each of a multiplicity of selected cells. The described honeycomb filters are often densely celled and may have transverse, cross-sectional cellular densities ranging upwards to about 100 cells/cm.sup.2 or more. Tolerances required both in the fabrication of masks and other tools and in the alignment of the masks or tools with each of a large number of selected cell ends at the end face are narrow, adding to filter manufacturing difficulties and expense. Moreover, due to manufacturing limitations, honeycomb structures typically cannot be fabricated with their cells in perfect alignment. Thus, where a honeycomb structure is formed with a multiplicity of cells having substantially square, transverse cross-sectional geometries and arranged in mutually parallel rows and columns, one cannot expect the thin walls forming the rows and columns of the adjoining cells to be perfectly straight as is desired. This lack of cellular uniformity limits the usefulness of or at least increases the difficulties involved in using the described masks and tools, many of which are essentially inflexible and cannot be adjusted to compensate for these imperfections. This condition further complicates and thus makes more exensive any automation of any of these described filter fabricating processes.
Another problem associated with many of these filter fabricating inventions is that the tool(s) or mask(s) typically can be aligned as easily with either of the two sets of alternate cells selected to be closed at each end face of the honeycomb structure. Both the applications Ser. No. 283,732 and 295,611 describe embodiments which can or must select mutually exclusive sets of cells for plugging at either end face of a honeycomb structure. The aforesaid application Ser. No. 283,735 describes methods and apparatus for achieving closure of mutually exclusive sets of cells at either end face of a honeycomb structure using particular embodiments of the flexible/elastic masks described and claimed in the aforesaid application Ser. No. 283,734. The remaining filter fabricating methods and apparatus referred to above require that registration of a tool or mask with mutually exclusive sets of cells ends be verified, typically by a worker installing or using the mask or tool, thus adding to filter manufacturing expense.
More recently, other solid particulate filter body configurations have been identified which have simplified, to some extent, filter fabricating processes. Another copending application Ser. No. 350,998, filed on Feb. 22, 1982 assigned to the assignee hereof and incorporated by reference, describes and claims solid particulate filters fabricated from matrices of interconnected thin walls having at least a sufficient amount of interconnected open porosity to allow fluid to flow through the greater as well as across the narrower dimensions of the thin walls, thereby obtaining filtration through all thin wall surfaces defining each inlet cell irrespective of the type of adjoining cell (i.e. inlet or outlet) with which the inlet cell shares its defining thin walls in common. This feature simplifies to some extent the filter fabrication process as it allows cells to be closed in rows, columns or other clusters, and thus reduces the necessity to deal with each cell of the structure separately. Yet another related copending application Ser. No. 350,995 also filed on Feb. 22, 1982, assigned to the assignee hereof and incorporated by reference, depicts and decribes other filter configurations provided with this increased thin wall porosity and having cells closed in clusters. None of the filter embodiments described in either of these applications, however, eliminates the necessity of aligning a mask or tool with the clusters of selected cell ends at either end face of the honeycomb structure or of verifying that the mask or tool has been aligned with mutually exclusive sets of cells at either end face of the structure.